For
By
Extension Horticulture Agent
Yellow Leaves on Evergreens Occur During Fall
Yellow leaves are showing up on several species of broadleaved evergreen shrubs this fall and in most cases, there is nothing wrong with them. This is the natural shedding some of the older leaves which will be replaced with next spring’s flush of growth.
The word evergreen might lead one to believe that the foliage is permanent. It’s true that evergreen shrubs retain green foliage through all seasons of the year, but they shed old leaves annually. Imagine what ten year old leaves would look like if they stayed on a plant for so long. They would be spotted, scarred and generally ugly.
The broadleaved evergreens include many of the most popular local landscape plants. These include species of gardenia, camellia, oleander, pittosporum, pyracantha, holly, aucuba and azalea.
This leaf shedding, which I prefer to call leaf exchanging, is especially evident on gardenias right now. The leaves of these plants are relatively large, smooth and take on a bright yellow color just before falling.
Several local gardeners have shown concern for their gardenias, wondering what is wrong with them. As long as the yellow leaves are found toward the inner parts of individual plants at this time of year, there is generally nothing to worry about.
Don’t confuse natural leaf drop with signs and symptoms of nutritional disorders, insect damage or root rots. The following signs are not due to changing weather and might require treatment: dead twigs and branches scattered throughout the plant canopy; the dying of leaves that begins at branch tips and progresses downward, and many leaves that turn white or yellow, yet the veins remain green.
Scattered dead twigs and branches sometimes indicate a scale insect infestation. Fall is a good time of year to control scales by applying horticultural oil emulsion spray. Dying terminal growth can be the result of extremely wet soil conditions. Evaluate your irrigation practices. Established shrubs should not be watered more than once or twice per week. White or yellow leaves, with the veins retaining green color sometimes indicates a minor element deficiency. Watch for a future gardening column on this subject.
Question of the Week: English ivy is growing up one of my trees. Will the ivy kill it?
Answer: A heavy growth of English ivy or any healthy vine can eventually weaken the tree. Due to the way that English ivy anchors itself to a tree, I doubt that it would girdle or “choke” it. Vine damage is more indirect. The leaves compete with the tree’s leaves by shading them and reducing photosynthesis. Also, as vines increase in age and size they add much weight to tree branches. When the vine’s leaves are wet they are extremely heavy and can result in broken branches.
Flowering
ornamental vines are becoming very popular.
They perform best when provided with support such as a trellis, fence or
arbor. Most prefer full sunlight, though
English ivy is an exception.